I want to create a delimiter between two regular paragraphs of text as in the end of page 6 of this pdf.

One way out could be the Vmatrix environment but then I dont know how to make the right delimiter disappear.
Quick googling suggested only the usual way of using \right. to make a delimiter disappear but that wont work here.

I used the framed package to define a dleftbar environment to enclose the contents using a double vertical rule; then, this environment was used in conjunction with the amsmath package to define some theorem-like structures (admitting page breaks):